column: add dense layout support

Normally all cells (and in turn columns) share the same width. This
layout mode can waste space because one long item can stretch our all
columns.

With COL_DENSE enabled, column width is calculated indepdendently. All
columns are shrunk to minimum, then it attempts to push cells of the
last row over to the next column with hope that everything still fits
even there's one row less. The process is repeated until the new layout
cannot fit in given width any more, or there's only one row left
(perfect!).

Apparently, this mode consumes more cpu than the old one, but it makes
better use of terminal space. For layouting one or two screens, cpu
usage should not be detectable.

This patch introduces option handling code besides layout modes and
enable/disable to expose this feature as "dense". The feature can be
turned off by specifying "nodense".

Thanks-to: Ramsay Jones <ramsay@ramsay1.demon.co.uk>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t9002-column.sh

@@ -90,6 +90,30 @@ EOF
 	test_cmp expected actual
 '
 
+test_expect_success '20 columns, nodense' '
+	cat >expected <<\EOF &&
+one    seven
+two    eight
+three  nine
+four   ten
+five   eleven
+six
+EOF
+	git column --mode=column,nodense < lista > actual &&
+	test_cmp expected actual
+'
+
+test_expect_success '20 columns, dense' '
+	cat >expected <<\EOF &&
+one   five  nine
+two   six   ten
+three seven eleven
+four  eight
+EOF
+	git column --mode=column,dense < lista > actual &&
+	test_cmp expected actual
+'
+
 test_expect_success '20 columns, padding 2' '
 	cat >expected <<\EOF &&
 one     seven
@@ -129,4 +153,28 @@ EOF
 	test_cmp expected actual
 '
 
+test_expect_success '20 columns, row first, nodense' '
+	cat >expected <<\EOF &&
+one    two
+three  four
+five   six
+seven  eight
+nine   ten
+eleven
+EOF
+	git column --mode=row,nodense <lista >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success '20 columns, row first, dense' '
+	cat >expected <<\EOF &&
+one   two    three
+four  five   six
+seven eight  nine
+ten   eleven
+EOF
+	git column --mode=row,dense <lista >actual &&
+	test_cmp expected actual
+'
+
 test_done